There are a number of medical interventions that are carried under fluoroscopy or angiography. In other words, real-time projection X-ray images are acquired to image the internals of the patient along with medical tools or devices introduced into the patient to achieve the intervention.
For example, in order to stem growth of cancerous tissue or of an AVM (arteriovenous malformation) its arterial feeders may be intentionally embolized to shut down the blood supply (AVM) and/or stop nutrient supply to the cancer or growth (such as in transcatheter arterial chemoembolization (TACE)). This type of intervention, called medical embolization, may be brought about by administering an embolization agent at a desired location (region of interest (ROI)) in the human body by way of a catheter tube. The embolization agent is essentially a liquid volume or mass of glue comprising small beads suspended in a carrier liquid through which the occlusion at the diseased location effected. During such embolization interventions it is pre-eminent to ensure that it is only the targeted arterial feeders that are blocked off but sound vessels are not. At present the position of emboli is monitored by acquiring one or more fluoroscopic projection images. Because of radiation opacity of the embolus and/or of the carrier fluid, projective “footprints” are discernible in said fluoroscopic images thereby providing clues to an interventionist radiological about the embolus' whereabouts.
Another example for an intervention that relies on image based support is Transcatheter Aortic Valve Implantation (TAVI). To evaluate the outcome of a TAVI procedure, a visual evaluation of valvular regurgitations is routinely performed using angiography. An injection of contrast agent is performed. The interventionist then visually examines angiogram frames for whether there is contrast agent back flow into the left ventricle to so determine a severity of the regurgitation (based on the amount of contrast in the ventricle, the proportion of the ventricle filled with contrast, etc.).
In the above two exemplary interventions and also in others, the image quality is often compromised by poor contrast in one or more motion layers viewed against a complex and cluttered background (spine, ribs, medical devices, etc.). In an attempt to improve the situation, Digital Subtraction Angiography (DSA) is sometimes used to achieve better image contrast. In traditional DSA, a mask image is subtracted from a contrast image (e.g. the angiogram or a fluoroscopic frame that captures the embolus, etc.). However due to complex motion patterns during the intervention, subtraction artifacts may be introduced by DSA which again undermines image quality.